The present invention relates to gas valves for use in gas-lift production wells wherein a fluid is produced from a subterranean formation through a production tube and gas is introduced into the production tube to enhance production.
In the course of pumping hydrocarbons from subterranean formations, the formation is typically under pressure which can be utilized to drive the desired fluid through a production tube and to the surface. As fluids are produced, the natural formation pressure tends to drop, and can reach a point where production is at undesirably low flow rates.
Various methods are utilized for enhancing production from such a well. One such method is gas-lift techniques wherein gas is introduced into the production tube at various points along the production tube so as to lighten the hydrocarbon within the production tube and enhance production.
In the course of injecting has into the production tube, it is desirable to maintain gas injection rates substantially constant so as to avoid erratic operation of the well. Gas is frequently provided by pumps and other units for injection into the well, the this typically provides the gas at fluctuating pressures and/or flow rates. This can least to unstable performance or a gas-lift well, which is certainly undesirable.
An unstable performance can be avoided by utilizing a valve at the point of injection and by establishing critical flow through the valve such that fluctuations in gas pressure upstream of the valve are not transmitted beyond the valve.
FIG. 1 illustrates a conventional square edged valve used for such a purpose. Unfortunately, with a valve structure as illustrated in FIG. 1, a large pressure differential is needed to reach critical flow, and the critical flow rate is not as large as would be desired.
FIG. 2 shows another prior art valve structure, which is also disclosed in U.S. Pat. No. 5,743,717. In this valve, an inlet nozzle and outlet venturi are provided, and this structure provides critical flow at a smaller pressure differential as compared to the structure FIG. 1. Unfortunately, the structure of FIG. 2 requires relatively complex techniques during manufacture so as to provide for the smooth inlet nozzle and the like, and this structure prevents satisfactory use of such a valve in gas-lift applications and as an unloading valve.
The need remains, therefore, for a cost effective valve which is suitable for providing critical flow at small pressure differential between injection pressure and tubing pressure, and which provides critical flow at a flow rate which is substantially higher than conventional square valves.
It is therefore the primary object of the present invention to provide such a valve.
It is a further object of the present invention to provide a valve which is excellent in providing critical flow at relatively small pressure differentials for use as a gas operation valve, and which also can be utilized as an unloading valve.
It is a further object of the present invention to provide a gas-lift system utilizing such a valve.
Other objects and advantages of the present invention will appear hereinbelow.
In accordance with the present invention, the foregoing objects and advantages have been readily attained.
According to the invention, a gas-lift valve is provided which comprises a valve member having an inner wall defining a flow passage having a longitudinal axis, said valve member having a planar inlet end and an outlet end, said inner wall diverging from said inlet end to said outlet end so that said flow rate passage increases in cross sectional area from said inlet end to said outlet end.
In further accordance with the invention, a gas-lift system for controlling flow from an external gas source into a production tube is provided, which system comprises a production tube for conveying fluid from a subterranean source to surface level; a conduit for communicating an interior of said production tube with a location exterior of said production tube; and a valve member positioned in said conduit and having an inner wall defining a flow passage having longitudinal axis, said valve member having a planar inlet end and an outlet end, said inner wall diverging from said inlet end to said outlet end so that said flow passage increases in cross sectional area from said inlet end to said outlet end.